One of the most interesting properties of the Stacks blockchain is the view of their nodes into the state of the Bitcoin blockchain. The view is available in the smart contract language and it is possible to verify on-chain that a Bitcoin transaction was actually mined as described earlier in this post.
The main part of the verification is implemented in a library contract (clarity-bitcoin-lib-v1.clar)
I reviewed an early state of a library that helps web developers to use the library. The git repo is here: https://github.com/web3devs/stacks-bitcoin-api
It helps to build the parameters required to call a Clarity smart contract that uses the bitcoin library contract. Any Bitcoin transaction can be verified that has 4 or less input parameters and 4 or less output parameters.
There are a few open issues to finalized the library that hopefully will be resolved in Q3 2022.
The library is built with the support of Stacks grant #426.